In addition to the built-in sensors, you can create your own sensors. Just write a script or a program and use it with a custom sensor. There are already many free, useful scripts, plugins, and add-ons for PRTG in the PRTG Script World. You can directly open the Script World from the Add Sensor dialog in the PRTG web interface.

Active Fileshare Sessions

Active Lync Users, Inbound/Outbound Calls

Active Windows Users

AD Group Membership

Advanced Exchange Server Metrics

Age of McAfee Anti-Virus Signatures

AllNet UPS

Altaro Hyper-V Backup Monitoring

Amazon AWS Costs

APC Battery Replacement

Aruba Wireless Controller Device Template

Atlantis ILIO

Automatic Services

AWS Costs Sensor

BGP Peer Status

Brocade Switch Device Template

BulkSMS Remaining Credits Sensor

Ceph Cluster Storage Python Sensor

Certain HTTP Response Code

Citrix Environments

Citrix NetScaler

Configured Remote Probes

DICOM and HL7

Dynamic Windows Processes

Exim Queue Length

Find Groups and Devices with Auto-Discovery Enabled

Google Search Appliance

Historic Windows Events

HP 3Par Enterprise Storage

HP ProCurve Switch Version and Model

HTTP Return Codes

Hyper-V Replication

iDirect Modem Sensor

IP Addresses of Hops

Kemp Load Balancer

Linux Distributions that are Incompatible with the SSH Disk Free Sensor